Add [Symbol.dispose] support for ref types

[yf-yang]

Calling .unref() is just fine, but sometimes it could be forgotten and cause memory leaks.

TC39 stage 3 proposal https://github.com/tc39/proposal-explicit-resource-management is aimed at solving the problem. We can add a Symbol.dispose method to those pathRef, pointRef, rangeRef to keep up with the spec.

The only possible problem here is that we don't know how Symbol.dispose is supported in different js runtimes. I believe latest browsers and node has already supported it, but not sure about previous versions. Can't find the info in CanIUse, either.

[work-in-progress-danny]

Seems related to #5726

[yf-yang]

Nope, just a standard compatible API